How'd I miss this thread? It does need at least a few cat's eye pics, though, since "chat"="cat" and "oy" comes from "oeil"=eye. Here are a few from my old photos – clouds have rolled in, so no new pics:

chrysoberyl, the original "cat's eye" gemstone

diopside

cat's eye emerald (bad pic, Colombia)

opal (Tanzania)

Glass Buttes cat's eye obsidian (the bright line rolls around even on a flat slab like this)

I think you're seeing parallax, not chatoyancy. There are some similarities in appearance but they're generally accepted as different optical properties. The direct translation of "chatoyancy" is "like a cat's eye," which requires straight fibers in a stone like chrysoberyl, tourmaline, tiger's-eye and a few others. http://en.wikipedia.org/wiki/Chatoyancy, tiger's-eye.

The parallax effect is a shadowy optical appearance in tightly-banded fortification agates like yours that moves as the stone is turned. Both are neat effects and well worth collecting.

Sugilite is not a chatoyant stone. There's no included fibers or crystals in your slab to create the effect. Sugilite is prized mainly for its color, the occasional presence of related minerals like Richterite and Bustamite, and for its rare translucent (gel) properties.

I don't believe that you have to have an actual cats eye effect to be considered chatoyant. Here's a repost of my idea of chatoyant, from my very first post that started this thread:

"Chatoyant stones are some of the most interesting and beautiful of the semi precious stones. The group of chatoyant stones includes such well known stones as Tiger Eye, Marra Mamba, Pietersite, Binghamite, Silk Stone, and varieties of common semiprecious stones like Malachite, Jade, and Obsidian. Chatoyant stones are those that can change in luster or color by orienting them differently to a light source. It is also what causes the Tiger Eye property which is a reflected streak of light from a chatoyant stone that is cut and polished into a cabochon."

Of the three qualities listed in a dictionary, the changing of the luster/color by changing the orientation to a light source, is the main quality that i use when determining if a stone is chatoyant. It is probably the case that most instances of luster/color change, could also lead to a tiger eye effect if properly prepared. There are other stone characteristics that are often confused as being chatoyant, a few that come to mind are Adularescence and labradorescence. In the case of Adularescence of Moonstone, you can get a cats eye effect when the milky line forms. So its a bit confusing out there. I tend to allow a broader definition and go with any stone that changes luster/color due to a change in the orientation of a light source. I have stones that are not known to be named, that are chatoyant and there are often instances of non chatoyant stones that will sometimes show some chatoyancy, like in the case of Chatoyant Malachite.

Please continue to add pics and comments to this thread. Next milestone, 11,000!!!! posts.